For image-based diagnosis of e.g. cerebral illnesses such as stroke, AVM (arterial-vascular malformation) or cancer-related illnesses, the established methods such as CT (computer tomography), MR (magnetic resonance) and also C-arm-based 3D imaging are available today. In relation to CT and MR, for example, reference is made to the brochure “CME Radiologie—Zerebrale Perfusion” by Horst Traupe, Schering and Thieme, 2005. This analysis method includes the analysis of a volume data record which features a multiplicity of voxels, wherein each voxel is assigned to a location in the three-dimensional (3D) space. A common feature of these techniques is that they supply morphological information about the examination object.
The prior art also discloses all variety of techniques which provide functional information about the examination object in the field of CT and MR imaging. With regard to the blood supply of the examination object, in particular, it is possible to determine its perfusion, the volume of blood contained, the so-called “mean transit time” and other parametric variables. Important information can be derived from the comparison between the various variables. Reference is made, for example, to the specialist article “CT-Perfusionsbildgebung bei zerebraler Ischämie” by Matthias König, Radiologie up2date 2/2001, pages 187 to 202, and to the specialist article “Perfusion CT: a worthwhile enhancement?” by K. A. Miles and M. R. Griffiths, The British Journal of Radiology, April 2003, pages 220 to 231.
The imaging techniques are generally used in a pre-intervention phase. Consequently, they are not available during a therapeutic intervention. Interventions are generally carried out in the angiography laboratory, which usually includes a C-arm-based x-ray system. Such x-ray systems make it possible to generate morphological images in the three-dimensional space, and also in principle to perform functional measurements. Reference is made to the reprint “AXIOM Artis FD Systems—DynaCT—A Breakthrough in Interventional 3D Imaging” by Patrick Kurp, originally published in Medical Solutions, January 2005, pages 46 to 51.
The generation of three-dimensional morphological images and also the taking of functional measurements are admittedly possible in principle using angiography facilities. As a result of the limited rotation speed and the associated limited temporal resolutions, however, the applicability is only restricted. Furthermore, a high radiation dose is applied, thereby strictly limiting the repeated use.
One possibility for overcoming the limited temporal resolution while nonetheless achieving a high spatial resolution is the use of scenes from projection recordings, preferably in the DSA mode (DSA=digital subtraction angiography). For example, reference is made to the specialist article “Estimating Perfusion Using X-Ray Angiography” by Hrvoje Bogunović and Sven Lon{hacek over (c)}arić, published in Proceedings of the 4th International Symposium on Image and Signal Processing and Analysis, 2005, pages 147 to 150. The projection recordings correspond to projection images featuring a multiplicity of pixels, wherein each pixel is assigned to a location in a two-dimensional projection plane and has a pixel data value. In this specialist article, an approach is described for qualitatively calculating and displaying perfusion-correlated parameters. The specification of the functional parameters of the examination object takes place for the pixels of the projection recordings depending on their pixel data values. The solution offered in the cited specialist article is firstly nonetheless subject to limitations, which could be removed in principle by the elimination of vessels. However, a means of eliminating vessels is not specified in the specialist article. Secondly, as a result of the projective nature of the recordings and the typical geometry of the examination objects, different organ paths are traversed by the x-rays which are used there and hence depending on the location in the image—variously large volumes of the examination object are observed. Without taking into consideration the observed volume in each case, the quantitative analysis therefore varies from pixel to pixel.
The specialist article “Integrating X-ray angiography and MRI for endovascular interventions” by T. P. L. Roberts et al., MEDICA MUNDI 44/3, November 2000, pages 2 to 9, discloses an analysis method for data of an examination object, wherein the data comprises at least one volume data record of the examination object and a number of two-dimensional projection images of the examination object. The volume data record features a multiplicity of voxels. Each voxel is assigned to a location in the three-dimensional space. Each projection image features a multiplicity of pixels. Each pixel is assigned to a location in a two-dimensional projection plane. It features a pixel data value in each case. The projection images are registered in relation to the volume data record. Depending on their pixel data values, at least one functional parameter of the examination object is specified for the pixels of the projection images.